This invention relates to two-cycle internal combustion engines of the lever type and, more particularly, to improvements to two-cycle internal combustion engines of the kind described in U.S. Pat. No. 3,608,530 issued on Sept. 28, 1971 to one of the present applicants.
In general, two-cycle engines of the lever type have opposed power cylinders and separate air or air-fuel charging cylinders and a lever system interconnecting the power and charging cylinder pistons with each other and with a crank shaft. In the engine described in the patent, the disclosure of which is hereby incorporated herein by reference, a plurality of power cylinders (preferably in multiples of four or eight) are so arranged in pairs that the cylinders of each pair are directly opposed in axially aligned relationship in a horizontal plane; in the eight-cylinder engine, four pairs of opposed cylinders are arranged in parallel side-by-side relationship in a common horizontal plane. A single charging cylinder is provided for each pair of opposed power cylinders and are arranged in parallel side-by-side relationship in a common vertical plane, with the axes of the charging cylinders extending vertically and intercepting the axes of the power cylinders at right angles. The piston rod of each charging cylinder is connected at its lower end to the connected outer ends of the piston rods of the horizontally opposed power cylinders. That is, the inner end of each of the three piston rods is pivotally connected to its respective piston and the outer end of each piston rod is pivotally connected to the corresponding outer ends of the other two piston rods.
The crankshaft of the engine is located above the horizontally opposed power cylinders and below the vertically extending charging cylinders. The piston rod of the charging cylinder is connected, at a point intermediate its ends, to an offset crank pin of the crankshaft, and functions as the operative lever of the lever system. In this arrangement, the inner end of the lever (connected to the piston rod of the charging cylinder) is its fulcrum end; the outer end of the lever (which is connected to the outer ends of the piston rods of the power cylinders) is its effort end; and the intermediate connection between the lever and the crankshaft is the load or work-applying portion of the lever. There is no fixed axis for any part of the lever: the fulcrum moves linearly in a vertical line, reciprocating between upper and lower positions; the load-applying portion rotates in a circular path about the axis of the crankshaft; and the effort end of the lever describes an orbital path. The axial alignment of the opposed power cylinders provides a direct thrust, inertia absorbing cushion in each cylinder of each pair of opposed cylinders so as to free the crankshaft from excess inertial loading and making feasible a stroke-to-bore ratio in the power cylinders as high as approximately 2:1.
While the feature of interposing a lever between the power pistons and the crankshaft is essential to achievement of a 2:1 stroke-to-bore ratio so as to make possible a high torque, low speed engine in a small package, the structure illustrated in the patent has a number of undesirable mechanical features which have not heretofore been successfully overcome. For example, the high profile of the vertically-oriented charging cylinders makes the engine relatively large, and the friction of the charging pistons, which are connected to the moveable fulcrum, placed an undesirably heavy load on the crankshaft, with resulting decrease in engine efficiency. The vertical orientation of the charging cylinders, together with their position above the crankshaft, makes it difficult to properly lubricate the charging cylinder pistons.
Also, due to the orientation of the charging cylinders relative to the power cylinders, the outer end of the piston rod of each of the opposed power cylinders and also the outer end of the piston rod of the associated charging cylinder are pivotably connected along the common axis of a connecting pin passing through aligned holes near the ends of each of the three piston rods, with the result that their other ends (i.e., the end connected to a piston) do not lie in the vertical plane defined by the central axes of the three cylinders. As a consequence, at least two the piston rods are necessarily bent along some portion of their length, thus requiring that forces other than compression and tension must be taken into account in the design of the piston rods.
A primary object of the present invention is to provide an improved lever-type engine which avoids the above-outlined undesirable features of the engine described in the aforementioned patent.
Another object of the invention is to provide a lever-type engine of the character described, wherein opposed power cylinders are axially aligned to provide a direct thrust and are supplied with air from a compressor driven in rotation by the crankshaft, thereby to eliminate the troublesome charging cylinders of the prior art engine.
Another object is to provide a lever-type engine of the character described, wherein the power cylinders are arranged in a horizontal plane disposed above the crankshaft and which takes advantage of the slidable fulcrum principle with a simple, relatively short connecting linkage between the power pistons and the crankshaft.